1. Field of the Invention
The present invention relates to a cooling air passage in a motor-driven tool having a cooling fan, such an impact driver or the like.
2. Description of the Related Art
A conventional motor-driven tool will be described referring to FIGS. 6 to 9. The conventional motor-driven tool as shown in FIGS. 6 and 7 has a substantially T-shape. In a body part composed of a housing 5 which is divided in two and constitutes a main body of the motor-driven tool (hereinafter referred to as “a housing”), there are arranged a motor which is a power source, a reduction gear mechanism, and so on, and in a handle part hanging down from the body part, there are arranged a trigger switch for supplying a power to the motor, and so on. There are also provided, in the above mentioned body part, a carbon brush block 8 for holding a carbon brush 17 which supplies a power to an armature 1 of the motor, and so on. These carbon brush block 8 and so on are clamped by the housing 5 to be held at a determined position in the housing 5. There are further formed a rib 5a in the housing 5 in order to receive and position a stator 3. Because the rib 5a supports the stator 3 at its left side face, an air entering from a suction port 21 provided in the housing 5 is blocked by the rib 5a and the stator 3, and flows along an outer peripheral wall of the stator 3 to the right in FIG. 7, as shown by an arrow B′ in FIG. 7. Then, the air flows between the stator 3 and the armature 1 to the left in FIG. 7, and thereafter, will be discharged from a discharge port 7 to an exterior of the housing 5. The carbon brush block 8 consists of a carbon tube 9, a carbon cap 18, a lead wire 19 and so on. This carbon brush block 8 is arranged in such a manner that the carbon brush 17 can be attached and detached from the exterior of the housing.
At a side of the armature 1 opposite to its output side, there is provided a cooling fan 2. When this cooling fan is rotated, an air around the cooling fan 2 is discharged from the discharge port 7 provided in the housing 5, and accordingly, a negative pressure is created in the housing 5 to form a difference in pressure between an inside and an outside of the housing. As the results, airs flow into the housing through suction ports 20 and 21 provided in the housing 5. The armature 1, the carbon brush 17, the carbon tube 9 and so on are cooled by these flows of the air (the arrows B, B′ in FIG. 7). The air flowing into the housing 5 from the suction port 20 is mainly used for cooling a commutator 11, the carbon brush 17, the carbon tube 9 and so on, while the air flowing into the housing 5 from the suction port 21 is mainly used for cooling the armature 1 which is a heat source.
The conventional motor-driven tool as shown in FIGS. 8 and 9 has a substantially T-shape. In a body part composed of a housing 5 constituting the main body of the motor-driven tool, there are arranged a motor which is a power source, a reduction gear mechanism, and so on, and in a handle part hanging down from the body part, there are arranged a trigger switch for supplying a power to the motor, and soon. There are also provided in the body part a carbon brush block 8 for holding a carbon brush 17 which supplies a power to an armature 1 of the motor, and so on. These carbon brush block 8 and so on are provided in a casing 22 which contains the armature 1 and a stator 3.
At a side of the armature 1 opposite to its output side, there is provided a cooling fan 2. When this cooling fan 2 is rotated, an air around the cooling fan 2 is discharged from a discharge port 7 provided in the casing 22 to an exterior of the casing 22, and accordingly, a negative pressure is created in the casing 22 to form a difference in pressure between an inside and an outside of the casing 22. As the results, airs flow into the casing 22 through suction ports 6 and 6′ provided in the casing 22. The armature 1, the carbon brush 17, the carbon tube 9 and so on are cooled by these flows of the air (arrows C, C′ in FIG. 9).
In the cooling structure of the motor-driven tool as shown in FIGS. 6 and 7, there has been a problem that because the air for cooling the armature (the arrow B′ in FIG. 7) flows along an outer periphery of the stator, an air passage (distance) from the suction port to the armature becomes long, resulting in a serious loss of pressure and decrease of cooling efficiency, and consequently, the armature will be burnt to be broken at an earlier stage.
On the other hand, in the cooling structure of the motor-driven tool as shown in FIGS. 8 and 9, because the air for cooling the armature is not an air passage flowing along the outer periphery of the stator, the armature can be cooled by the air flow as shown by the arrow C in FIG. 9. However, there has been a problem that since the air entering into the casing from the suction port at the carbon brush side (the arrow C′ in FIG. 9) flows into a large space which is formed between the casing and the carbon brush and so on, velocity of the flow will be lowered, and strong cooling air cannot be applied to the commutator, the carbon brush and the carbon tube. As the results, heat generation of the carbon brush and the carbon tube cannot be prevented, resulting in fusion of the carbon cap and so on.